A charge air cooler is often included in a boosted engine system to improve a combustion efficiency of the engine. Intake air entering the engine may be compressed, or boosted, by a turbocharger compressor prior to combustion, resulting in an increase in temperature of the air. The warmed air may be channeled through the charge air cooler (CAC) to cool the air before being delivered to an intake manifold for subsequent mixing with fuel followed by ignition of the mixture at the engine cylinders. Cooling the boosted air increases its density so that a greater number of air molecules are introduced to the cylinders per unit volume of air, resulting in a proportional increase in a power output of the engine that is derived by combustion of the air-fuel mixture. Furthermore, cooling the boosted air decreases the amount of NOx emitted as a combustion product and reduces a likelihood of engine knock which may otherwise lead to degradation of engine performance.
The CAC, also known as an intercooler or aftercooler, is a heat exchange device formed from a thermally conductive material such as aluminum or another type of metal. A surface of the CAC is often arranged in a front compartment of a vehicle, perpendicular to air flow generated during vehicle navigation, to facilitate air-to-air cooling of the boosted air passing through the CAC. The CAC is often configured with alternating rows of tubes and fins that are held together by two headers plates with tanks welded to the headers. The tubes may be fluidically coupled at either end to one of the tanks so that air delivered to a first, inlet tank is channeled through the tubes, combined at a second, outlet tank and released from the CAC to be delivered to the intake through an intake passage. The fins may increase a surface area of the CAC that comes into contact with the cooling cross-air flow. Heat is thus transferred from the warm boosted air, to the cooler surfaces of the CAC tubes which are, in turn, cooled by ram air and the engine cooling fan.
The cooling of the boosted air, however, may lead to condensation issues. For example, in humid climates, a temperature of the relatively moist air cooled by the CAC may fall below a dew point of the air. This may result in water droplets condensing within channels of the CAC, the intake passage, or intake manifold. During periods of high boost demand driving increased air flow through the CAC, the water droplets may be purged into the engine cylinders during an intake cycle of the cylinders, leading to misfiring at the cylinders or hydrolock.
In addition, cooling the boosted air below a threshold, such as the dew point, may lower a manifold charge temperature of the engine. While lower charge air (e.g. boosted air ignited at the engine cylinders) temperature may enhance engine performance and reduce NOx emissions, a concomitant decrease in combustion temperature may lead to undesirably high levels of carbon monoxide and hydrocarbon discharged from the engine exhaust.
Other attempts to address overcooling of air flowing through the CAC include adapting the engine with a bypass system to allow warmed air to reach the intake manifold. One example approach is shown by Tussing et al. in U.S. Pat. No. 7,007,680. Therein, a bypass line diverts boosted air around a charge air cooler. Air flow through the bypass is controlled via a bypass valve that is actuated by a bypass controller. The bypass controller is configured to operate the bypass valve based on an intake manifold temperature and the bypass valve includes rotatable valve plates that are actuated by a device such as a solenoid or motor. Warmed air is diverted around the CAC and mixed with air exiting the CAC to maintain the temperature of the intake manifold above a dew point.
However, the inventors herein have recognized potential issues with such systems. As one example, when at least a portion of the intake air is diverted to the bypass around the CAC, the amount of air passing through the CAC is proportionally reduced. The air is sent to all channels of the CAC which are exposed to ram air (and fanned air) at ambient temperature. During low mass flow rates, a temperature difference between the bypassed air and cooled air may be increased due to longer contact between air molecules and cooling surfaces of the CAC channels, thus decreasing the modulating effect of the bypassed air on the manifold charge temperature (MCT). Furthermore, regulation of air flow between the bypass and CAC channels may introduce undesirable complexity of control by burdening the system with additional sensors and valves.
In one example, the issues described above may be addressed by a cooling system of an engine comprising an intake passage configured to deliver boosted air to an intake manifold of the engine, a charge air cooler coupled to the intake passage, wherein the charge air cooler has an integrated bypass, a plurality of cooling channels, and a dual-gate mechanism arranged at an outlet end of the charge air cooler, the dual-gate mechanism including a first gate controlling flow of boosted air from the integrated bypass to the outlet and a second gate dividing the plurality of cooling channels into open channels and blocked channels, the blocked channels fluidically blocked from flowing intake air to the outlet. In this way, the MCT may be regulated by a single device actuated in response to output from sensors already existing in the engine system.
As one example, the variable thermal capacity charge air cooler (VTC-CAC) may be adapted with an integrated bypass and a dual-gate mechanism that portions air flow between the integrated bypass and the cooling channels of the VTC-CAC. The dual-gate mechanism is arranged in a header tank of the VTC-CAC and comprises a first gate that adjusts a number of cooling channels open to air flow and a second gate that moderates an opening to the bypass. Movement of both gates is caused by a rotating screw that extends across the header tank and includes different thread pitches to achieve a difference in a speed of movement between the first and second gates (e.g., the first gate may move along a first section of the rotating screw that has a first thread pitch and the second gate may move along a second section of the rotating screw that has a second thread pitch, different than the first thread pitch). By adapting an engine system with the VTC-CAC, the MCT may be controlled using a single inexpensive device, and a likelihood of condensation forming and/or accumulating within the intake passage or intake manifold is reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.